The present invention relates to a pattern matching system, and more particularly to a sewing machine with a pattern matching system for matching the patterns on two fabric pieces while the fabric pieces are being sewn to each other.
One conventional sewing machine with a pattern matching capability is disclosed in Japanese Laid-Open Patent Publication No. Sho60-153896. The disclosed sewing machine has optical sensors for detecting two respective fabric pieces, the optical sensors being located in front of a position where the fabric pieces are to be sewn to each other in overlapping relationship. The optical sensors detect light rays reflected from the fabric pieces. The intensities of the reflected light rays vary depending on patterns on the fabric pieces. Therefore, when the reflected light rays are detected by the optical sensors in synchronism with the feeding of the fabric pieces, the optical sensors detect patterns of light intensity variations corresponding to the fabric patterns. The detected patterns of light intensity variations are compared with each other, and any deviation or misalignment between the fabric pieces is calculated from the difference or shift between the compared patterns. The rate at which the two fabric pieces are fed relatively to each other is then adjusted in order to eliminate the mismatch between the fabric patterns, for thereby automatically matching the fabric patterns.
Japanese Laid-Open Patent Publication No. Heil-192387 discloses a pattern matching system which has R, G and B color sensors for detecting color differences between the colors of patterns. Based on the detected color differences, it is determined how color saturations are changed on the patterns of fabrics, to thereby calculate any mismatch between the patterns.
The conventional pattern matching systems thus utilize optical information of the patterns on fabric pieces that represents only lightness which indicates the brightness of colors and saturation which indicates the depth of colors. The prior pattern matching systems do not detect hue which indicates the types of colors, i.e., the kind by which one color is distinguished from another color. Therefore, the conventional pattern matching systems have been unable to detect any mismatch between patterns which have the same lightness and saturation, but are of different hues.